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Synaptic dysfunction is recognized as an early step in the pathophysiology of parkinsonism. Several genetic mutations affecting the integrity of synaptic proteins cause or increase the risk of developing disease. We have identified a candidate causative mutation in synaptic "SH3GL2 Interacting Protein 1" (SGIP1), linked to early-onset parkinsonism in a consanguineous Arab family. Additionally, affected siblings display intellectual, cognitive, and behavioral dysfunction. Metabolic network analysis of [ 18 F]-fluorodeoxyglucose positron emission tomography scans shows patterns very similar to those of idiopathic Parkinson's disease. We show that the identified SGIP1 mutation causes a loss of protein function, and analyses in newly created Drosophila models reveal movement defects, synaptic transmission dysfunction, and neurodegeneration, including dopaminergic synapse loss. Histology and correlative light and electron microscopy reveal the absence of synaptic multivesicular bodies and the accumulation of degradative organelles. This research delineates a putative form of recessive parkinsonism, converging on defective synaptic proteostasis and opening avenues for diagnosis, genetic counseling, and treatment., Competing Interests: Declaration of interests The authors declare no competing interests., (Copyright © 2024 The Author(s). Published by Elsevier Inc. All rights reserved.)

The minor phospholipid phosphatidylinositol 4,5-bisphosphate [PI(4,5)P 2 ] is crucial for neurotransmission and has been implicated in Parkinson's disease. Here, we present a staining protocol for the analysis of activity-dependent changes of PI(4,5)P 2 at synapses. We describe steps for stimulating and fixing murine hippocampal neurons, staining with probes for PI(4,5)P 2 and a synaptic marker, and analysis by high-resolution microscopy. Our approach gives insights into local PI(4,5)P 2 synthesis and turnover at synapses and can be extended to phosphoinositide lipids other than PI(4,5)P 2 . For complete details on the use and execution of this protocol, please refer to Bolz et al. 1 ., Competing Interests: Declaration of interests The authors declare no competing interests., (Copyright © 2024 The Author(s). Published by Elsevier Inc. All rights reserved.)

Exocytosis and endocytosis are essential physiological processes and are of prime importance for brain function. Neurotransmission depends on the Ca 2+ -triggered exocytosis of synaptic vesicles (SVs). In neurons, exocytosis is spatiotemporally coupled to the retrieval of an equal amount of membrane and SV proteins by compensatory endocytosis. How exocytosis and endocytosis are balanced to maintain presynaptic membrane homeostasis and, thereby, sustain brain function is essentially unknown. We combine mouse genetics with optical imaging to show that the SV calcium sensor Synaptotagmin 1 couples exocytic SV fusion to the endocytic retrieval of SV membranes by promoting the local activity-dependent formation of the signaling lipid phosphatidylinositol 4,5-bisphosphate (PI(4,5)P 2 ) at presynaptic sites. Interference with these mechanisms impairs PI(4,5)P 2 -triggered SV membrane retrieval but not exocytic SV fusion. Our findings demonstrate that the coupling of SV exocytosis and endocytosis involves local Synaptotagmin 1-induced lipid signaling to maintain presynaptic membrane homeostasis in central nervous system neurons., Competing Interests: Declaration of interests The authors declare no competing financial interests., (Copyright © 2023 Elsevier Inc. All rights reserved.)

Pathogenic α-synuclein and tau are critical drivers of neurodegeneration, and their mutations cause neuronal loss in patients. Whether the underlying preferential neuronal vulnerability is a cell-type-intrinsic property or a consequence of increased expression levels remains elusive. Here, we explore cell-type-specific α-synuclein and tau expression in human brain datasets and use deep phenotyping as well as brain-wide single-cell RNA sequencing of >200 live neuron types in fruit flies to determine which cellular environments react most to α-synuclein or tau toxicity. We detect phenotypic and transcriptomic evidence of differential neuronal vulnerability independent of α-synuclein or tau expression levels. Comparing vulnerable with resilient neurons in Drosophila enabled us to predict numerous human neuron subtypes with increased intrinsic susceptibility to pathogenic α-synuclein or tau. By uncovering synapse- and Ca 2+ homeostasis-related genes as tau toxicity modifiers, our work paves the way to leverage neuronal identity to uncover modifiers of neurodegeneration-associated toxic proteins., Competing Interests: Declaration of interests P.V. is the scientific founder of Jay Therapeutics., (Copyright © 2023 The Authors. Published by Elsevier Inc. All rights reserved.)

Neuronal networks maintain stable activity around a given set point, an enigmatic variable in homeostatic systems. In this issue of Neuron, Styr et al. (2019) now show that set points are regulated by mitochondria and propose a potential strategy to treat refractory forms of epilepsy., (Copyright © 2019 Elsevier Inc. All rights reserved.)

Neurotransmission is based on the exocytic fusion of synaptic vesicles (SVs) followed by endocytic membrane retrieval and the reformation of SVs. Recent data suggest that at physiological temperature SVs are internalized via clathrin-independent ultrafast endocytosis (UFE) within hundreds of milliseconds, while other studies have postulated a key role for clathrin-mediated endocytosis (CME) of SV proteins on a timescale of seconds to tens of seconds. Here we demonstrate using cultured hippocampal neurons as a model that at physiological temperature SV endocytosis occurs on several timescales from less than a second to several seconds, yet, is largely independent of clathrin. Clathrin-independent endocytosis (CIE) of SV membranes is mediated by actin-nucleating formins such as mDia1, which are required for the formation of presynaptic endosome-like vacuoles from which SVs reform. Our results resolve previous discrepancies in the field and suggest that SV membranes are predominantly retrieved via CIE mediated by formin-dependent actin assembly., (Copyright © 2017 Elsevier Inc. All rights reserved.)

Neurotransmission depends on presynaptic membrane retrieval and local reformation of synaptic vesicles (SVs) at nerve terminals. The mechanisms involved in these processes are highly controversial with evidence being presented for SV membranes being retrieved exclusively via clathrin-mediated endocytosis (CME) from the plasma membrane or via ultrafast endocytosis independent of clathrin. Here we show that clathrin and its major adaptor protein 2 (AP-2) in addition to the plasma membrane operate at internal endosome-like vacuoles to regenerate SVs but are not essential for membrane retrieval. Depletion of clathrin or conditional knockout of AP-2 result in defects in SV reformation and an accumulation of endosome-like vacuoles generated by clathrin-independent endocytosis (CIE) via dynamin 1/3 and endophilin. These results together with theoretical modeling provide a conceptual framework for how synapses capitalize on clathrin-independent membrane retrieval and clathrin/AP-2-mediated SV reformation from endosome-like vacuoles to maintain excitability over a broad range of stimulation frequencies., (Copyright © 2014 Elsevier Inc. All rights reserved.)